Bi-radial pop-on cervical bone anchor

ABSTRACT

A cervical polyaxial bone anchor includes a longitudinal connecting member receiver structure and a cooperating shank. The shank has a body and an integral head with first and second spherical surfaces of different radii and a plurality of spaced curvate apertures for receiving portions of the longitudinal connecting member to result in a greater angle of inclination of the shank with respect to the receiver. The receiver has an upper channel and a lower cavity that further includes an expansion area and an operational seat for a split retainer ring that captures and fixes the shank head within the receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Ser. No.61/925,420, filed Jan. 9, 2014, which is incorporated by referenceherein.

BACKGROUND OF THE INVENTION

The present invention is directed to polyaxial bone anchors for use inbone surgery, particularly spinal surgery and particularly to such boneanchors with retainers for capturing and retaining a bone screw shankhead in the receiver member assembly and later fixing the bone screwshank with respect to the receiver assembly.

Bone screws are utilized in many types of spinal surgery in order tosecure various implants to vertebrae along the spinal column for thepurpose of stabilizing and/or adjusting spinal alignment. When vertebraeof the cervical spine are involved, the connecting structure orstructures commonly include a plate and cooperating relatively smallerscrews. When the connector is in the form of a rod, both closed-endedand open-ended bone screws are known with open-ended screws beingparticularly well suited for connections to rods and connector armsbecause such rods or arms do not need to be passed through a closedbore, but rather can be laid or urged into an open channel within areceiver or head of such a screw. Generally, the screws must be insertedinto the bone as an integral unit along with the head, or as apreassembled unit in the form of a shank and pivotal receiver, such as apolyaxial bone screw assembly.

Typical open-ended bone screws include a threaded shank with a pair ofparallel projecting branches or arms which form a yoke with a U-shapedslot or channel to receive a rod. Hooks and other types of connectors,as are used in spinal fixation techniques, may also include similar openends for receiving rods or portions of other fixation and stabilizationstructure.

A common approach for providing vertebral column support is to implantbone screws into certain bones which then in turn support a longitudinalstructure such as a rod, or are supported by such a rod. Bone screws ofthis type may have a fixed head or rod receiver relative to a shankthereof, or may be of a polyaxial screw nature. In the fixed bonescrews, the rod receiver head cannot be moved relative to the shank andthe rod must be favorably positioned in order for it to be placed withinthe receiver head. This is sometimes very difficult or impossible to do.Therefore, polyaxial bone screws are commonly preferred. Open-endedpolyaxial bone screws typically allow for a loose or floppy rotation ofthe head or receiver about the shank until a desired rotational positionof the receiver is achieved by fixing such position relative to theshank during a final stage of a medical procedure when a rod or otherlongitudinal connecting member is inserted into the receiver, followedby a locking screw or other closure. This floppy feature can be, in somecases, undesirable and make the procedure more difficult, but desirablein other situations.

SUMMARY OF THE INVENTION

An embodiment of the present invention is a polyaxial spinal bone screwassembly for receiving and fixing placement of a longitudinal connectingmember such as a rod. The assembly includes a bone screw shank having abody for insertion into bone integral with an upper portion or head. Theshank head includes a top convex partially spherical first surfacehaving a first radius and a lower convex partially spherically shapedsurface having a second radius. A third annular surface extendsoutwardly from the first surface and terminates at the second surface ata spheric perimeter or edge. At least one and up to a plurality ofspaced concave surface features are formed through the edge and thusinto the annular and lower spherical surfaces. A rod or otherlongitudinal connector receiver structure has a pair of arms forming achannel as well as base that defines a cavity. The cavity is sized toallow for pivotal movement of the shank first and second surfaces therewithin. A lower opening communicates with the cavity and an exterior ofthe receiver opposite the pair of arms. The cavity communicates with thechannel. The receiver cavity is further defined by a lower seat and anexpansion area located above the lower seat. The bone screw head isuploaded and received in the cavity through the lower opening. Theassembly further includes an open and resilient ring-like retainerreceivable in the cavity and outwardly biased against the receiver infixed relation thereto at the receiver seat when the shank head iscaptured in the receiver and fixed against the retainer by a downwardforce placed directly on the head by a rod or other longitudinalconnecting member so as to fix or lock an angular position of thereceiver relative to the shank. The retainer is expandable about theshank head at the receiver cavity expansion area during uploading of theshank head through the receiver lower opening. Prior to locking, theshank head is in sliding, pivotable relation with the retainer and theretainer is rotatable with respect to the receiver. Also, while still inan unlocked position a portion of the rod may be received in an areadefined by one of the shank concave surface features to provide anincreased angle of articulation between the shank and the receiver.Thereafter, another portion of the rod may then be fixed into lockingengagement with the shank first convex surface.

Objects of the invention include providing apparatus and methods thatare easy to use and especially adapted for the intended use thereof andwherein the tools are comparatively inexpensive to produce. Otherobjects and advantages of this invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded and partial front elevational view of a polyaxialbone screw assembly according to an embodiment of the present inventionincluding a shank, an open retainer and a receiver and further showing acooperating rod and closure top shown with portions broken away to showthe detail thereof.

FIG. 2 is an enlarged and partial perspective view of the shank of FIG.1.

FIG. 3 is an enlarged top plan view of the shank of FIG. 2.

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3.

FIG. 5 is an enlarged perspective view of the receiver of FIG. 1.

FIG. 6 is a top plan view of the receiver of FIG. 5.

FIG. 7 is a bottom plan view of the receiver of FIG. 5.

FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG. 6.

FIG. 9 is a cross-sectional view taken along the line 9-9 of FIG. 6.

FIG. 10 is an enlarged perspective view of the open retainer of FIG. 1.

FIG. 11 is a reduced top plan view of the retainer of FIG. 10.

FIG. 12 is an enlarged and partial cross-sectional view taken along theline 12-12 of FIG. 11.

FIG. 13 is a reduced front elevational view of the receiver and retainerof FIG. 1 shown in a stage of assembly, the retainer shown in phantom inan earlier stage of assembly and the receiver shown with portions brokenaway to show the detail thereof.

FIG. 14 is a front elevational view with portions broken away of thereceiver and retainer of FIG. 13 and also showing the shank if FIG. 1 inan initial approach for assembly with the retainer, the shank being inpartial front elevation.

FIG. 15 is an enlarged and partial front elevational view with portionsbroken away of the receiver, retainer and shank of FIG. 14 and furthershowing the shank in an early stage of assembly with the retainerwherein the retainer is pushed upwardly against an inner surface of thereceiver.

FIG. 16 is an enlarged and partial front elevational view with portionsbroken away, similar to FIG. 15, showing a head of the shank in asubsequent stage of assembly with the retainer, pressing the retaineroutwardly to a configuration of maximum expansion against the receiver.

FIG. 17 is a partial front elevational view with portions broken away,similar to FIG. 16, showing the head of the shank pressed through theretainer and the retainer resiliently returned to a neutral or nearneutral configuration.

FIG. 18 is a partial front elevational view with portions broken away,similar to FIG. 17, showing the shank head lowered to a seated positionon the retainer.

FIG. 19 is a reduced and partial perspective view with portions brokenaway of the assembly as shown in FIG. 18 and further showing a shankdriver tool, also in partial perspective view.

FIG. 20 is an enlarged and partial perspective view with portions brokenaway of the assembly of FIG. 19, showing the driver engaged with theshank to drive the shank into a vertebra, shown in a partial andpartially schematic view.

FIG. 21 is a reduced and partial cross-sectional view taken along theline 21-21 of FIG. 20.

FIG. 22 is a reduced and partial perspective view of the assembly ofFIG. 20 further shown assembled with the rod and closure of FIG. 1, alsoin perspective view, the rod in phantom to show details of the assembly.

FIG. 23 is an enlarged and partial side elevational view with portionsbroken away of the assembly of FIG. 22, but with the shank pivoted to aforty-four degree angle with respect to the receiver in the sagittalplane with the shank directed caudally, the rod in phantom to showdetails of the assembly.

FIG. 24 is a reduced and partial rear elevational view of the assemblyof FIG. 23 with portions of the receiver broken away to show details ofthe assembly.

FIG. 25 is an enlarged and partial side elevational view with portionsbroken away of the assembly of FIG. 22, but with the shank pivoted to aforty-four degree angle with respect to the receiver in the sagittalplane with the shank pivoted in a cephalic direction, the rod in phantomto show details of the assembly.

FIG. 26 is a reduced and partial rear elevational view of the assemblyof FIG. 25 with portions of the receiver broken away to show details ofthe assembly.

FIG. 27 is an enlarged and partial front elevational view with portionsbroken away of the assembly of FIG. 22 but with the shank pivoted to aforty-four degree angle with respect to the receiver in the transverseplane.

FIG. 28 is an enlarged and partial side elevational view with portionsbroken away of the assembly of FIG. 22 but with the shank rotatedslightly and then pivoted to a twenty-four degree angle with respect tothe receiver in the sagittal plane, the rod in phantom to show detailsof the assembly.

FIG. 29 is a reduced and partial rear elevational view of the assemblyof FIG. 28 with portions of the receiver broken away to show the detailof the assembly.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the bone attachment structures in actual use.

With reference to FIG. 1, the reference number 1 generally represents apolyaxial bone screw apparatus or assembly according to an embodiment ofthe present invention that includes a shank 4 that further includes abody 6 integral with an upwardly extending upper portion or head-likecapture structure 8; a receiver 10; and an open ring retainer structure12. The receiver 10 and retainer 12 are initially assembled by thevendor and may be further assembled with the shank 4 either by thevendor or by a user prior to or after implantation of the shank body 6into a vertebra 17, as will be described in greater detail below. Thus,when desired, the shank 4 may be implanted into a vertebra first,followed by assembly with the other components. Even though such aprocedure might not at first blush appear desirable on the smaller, morefragile cervical vertebrae, due to the small size of the assembly 1 andthat only between about forty and about fifty inch pounds of torque isrequired for attaching a closure structure 18 to the receiver 10 tocapture and fix a longitudinal connecting member, such as a rod 21 tothe assembly 1, the initial posting or implantation of the shank 4followed by a push- or snap-on assembly with the receiver 10 isacceptable and may be a desired procedure in some circumstances. FIG. 1further shows such closure structure 18 for capturing the longitudinalconnecting member, for example, shown as a 3.5 millimeter diameter rod21 which in turn engages the shank head 8 that in turn presses intofixed frictional contact with the retainer 12, so as to capture, and fixthe longitudinal connecting member 21 within the receiver 10 and thusfix the member 21 relative to the vertebra 17.

The illustrated rod 21 is hard, stiff, non-elastic and cylindrical;however, it is foreseen that in other embodiments, the rod 21 may beelastic, deformable and/or of a different cross-sectional geometry.Although a 3.5 mm diameter rod is shown, the rod for use with thecervical assembly 1 could be smaller or bigger, with diametermeasurements of 3.0 mm, 3.75 mm and 4.0 mm also being common (and withthe receiver 10 being sized accordingly to cooperate with such diametersize). In some embodiments, the bone screw assembly 1 may also cooperatewith soft connecting systems, such as spinal connectors having rigidsleeves for placement within bone screw receivers in lieu of a rod, suchsleeves including through bores for receiving a tensioned cord, forexample.

As will be described in greater detail below the receiver 10 and thehead 8 of the shank 4 cooperate in such a manner that the receiver 10and the shank 4 can be secured at a plurality of different angles,articulations and rotational alignments relative to one another andwithin a selected range of angles both from side to side and from frontto rear, to enable flexible or articulated engagement of the receiver 10with the shank 4 until both are locked or fixed relative to each othernear the end of an implantation procedure. The drawings at FIGS. 19-21also illustrate a driver, generally 24 for use with the assembly 1 aswill be described in greater detail below.

The shank 4, best illustrated in FIGS. 1-4, is elongate, the shank body6 being only partially shown in the drawing figures. The body 6 iselongate and further includes one or more helically wound threads forbone engagement that are known in the art of pedicle screws, inparticular smaller screws sized and shaped for use on the cervicalspine. An example of a larger pedicle screw shank for use with someembodiments of the invention is illustrated, for example, in U.S. Pat.No. 6,726,689, which is also incorporated herein by reference to provideexamples of flange form guide and advancement structures for use withreceivers 10 and closures 18 of embodiments of the invention. Duringuse, the body 6 utilizing the thread or threads (not shown) for grippingand advancement is implanted into the vertebra 17 (e.g., see FIG. 20)leading with a tip of the shank 6 and driven down into the vertebra withan installation or driving tool, such as the tool 24, so as to beimplanted in the vertebra to a location at or near a neck thereof, asmore fully described in the paragraphs below. The shank 4 has anelongate axis of rotation generally identified by the reference letterA.

A neck 26 extends axially upward from the shank body 6. The neck 26 maybe of the same or of a slightly reduced radius as compared to anadjacent upper end or top of the body 6 where the thread or threadsterminate. Extending axially upwardly and radially outwardly from theneck 26 is the shank upper portion or head 8 that provides a connectiveor capture apparatus disposed at a distance from the threaded portion ofthe shank 6 and thus at a distance from the vertebra 17 when the body 6is implanted in such vertebra.

The shank upper portion or head 8 is configured for engagement betweenthe portion 8 and the retainer 12 (ultimately an operative fixed,frictional engagement) and a pivotable connection between the shank 4and the receiver 10 prior to fixing of the shank 4 in a desired positionwith respect to the receiver 10. The shank head or upper portion 8 has afirst outer, convex and substantially spherical surface 34 that extendsoutwardly and upwardly from the neck 26. A dotted line H1 in FIG. 1indicates a hemisphere of the lower spherical surface 34 that has amaximum or major diameter D at such hemisphere H1 as shown in FIG. 4. Aradius R1 shown in FIG. 4 is the radius of the surface 34 at the majordiameter D so D=2R1. The spherical surface 34 radius R1 is configuredfor frictional sliding and then ultimate fixed cooperation with theretainer 12 as will be discussed more fully in the paragraphs below. Theshank spherical surface 34 is locked into place at the retainer 12 andnot by inner surfaces defining the receiver 10 cavity, the shank head 8being held in spaced relation with the receiver 10 by the retainer 12.The spherical surface 34 shown in the present embodiment issubstantially smooth, but in some embodiments may include a rougheningor other surface treatment to enhance frictional engagement with theretainer 12. The surface 34 terminates at a circular spheric edge 36that extends around a perimeter of the surface 34 and intersects withand also partially defines an outer perimeter of a discontinuous annularsurface 38 located spaced from and above the hemisphere H1. The annularsurface 38 and the adjacent spherical surface have formed thereon aplurality of uniformly formed and spaced curvate concave surfaces 40 aswell as a multi-pronged drive receiving feature, generally 42, that willbe described in greater detail below. The surface 38 is substantiallyplanar and disposed perpendicular to the axis A. The surface 38 extendsradially inwardly of the spherical surface 34 starting at the sphericedge 39 and terminates at a second convex and substantially sphericalupper surface or dome 44. The dome 44 has a radius R2 that is smallerthan the radius R1 of the spherical surface 34. Both the radii R1 and R1are measured from the shank central axis A. The domed surface 44 radiusis configured such that the rod 21 directly engages and is fixableagainst the surface 44 at any and all operative angular configurationsof the shank 4 with respect to the receiver 10. The illustrated domedsurface 44 is smooth. However, the surface 44 may include ridges, aroughening or other surface treatment to provide enhanced frictionalcontact between the rod 21 and the surface 44.

With further reference to FIGS. 2 to 4, there are six substantiallyevenly spaced apertures or cut-out surfaces 40 of identical orsubstantially similar size and shape that are formed into the shank headsurfaces 34 and 38 and thus into the perimetric spheric edge 36. Thus,the loading edge 36 that is substantially circular and located above thehemisphere H1 is made discontinuous by the six arcuate surfaceformations 40. Three of the surface features 40 further include a driveslot 48 of the drive feature 42 as will be described in greater detailbelow. Each of the surfaces 40 is sized and shaped so as to provide apartially curved or partially cylindrical seat to receive a portion ofthe rod 21 as shown, for example in FIGS. 23-25 to allow for anincreased or maximum angle of inclination of the shank 4 with respect tothe receiver 10, which in the illustrated embodiment is approximatelyforty-four degrees. Thus, as shown in FIG. 4 each surface 40 isconfigured to receive the rod 21 along or near a line M that forms anangle N with respect to the shank axis A that in the illustratedembodiment is approximately forty-four degrees. It is foreseen that inother embodiments of the invention the angle N may be greater orsmaller. However, for angles greater than forty-four degrees, thecylindrical or curved cut-out area provided by each surface portion 42would also be wider which might eliminate or substantially reduce thesize of the annular surface 38 and thus the loading edge 36 of thespherical surface 34 located between each of the curved cut-outs 40.Such a decrease of the loading edge 36 located between each surfacefeature 40 would not be desirable as the spheric loading edge 36 and thespherical loading surfaces 34 located adjacent and below the edge 36 aresized for securely retaining the head 8 within the ring 12 and thusprohibiting pull-out of the shank head 8 from the receiver 10 when theshank 4 is pivoted at higher angles such as the forty-four degree angleshown in FIG. 23, for example. It is noted that in other embodimentsmore or fewer formations 40 may be used. The illustrated combination ofspaced concave surface formations 40, each with adjacent sphericalsurface portions 34 that terminate at the spheric edge 36,advantageously result in the bi-radial shank 4 that may be pivoted to upto about 44 degrees with respect to a cooperating rod 21 at a pluralityof locations on the shank head 8 and thus at a plurality of positionswith respect to the receiver 10 while keeping such shank head 8 securelywithin the receiver 10. It is noted that the term bi-radial in thisapplication may apply to two different aspects of the shank head 8. In afirst aspect, the shank head 8 has a first spherical surface 34 with afirst radius R1 and a second spherical surface 44 or dome that engagesthe rod that has a second, smaller radius R1. In a second aspect, theillustrated shank 4 may be described as having a bi-radial symmetrybecause the concave cuts or surface formations 40 are located oppositeone another on either side of the axis A and one surface portion 34having the upper support edge 36 is located adjacent to and between eachformation 40.

As best shown in FIG. 3, the internal drive feature 42 that includes thethree drive slots or grooves 48 is formed in an upper portion of thehead 8, specifically in the domed surface 44, the annular surface 38 andthree of the concave features 40. Each drive slot 48 includes a countersunk substantially planar base 50 an inner planar wall 52 and planaropposed side walls 54. Each slot 48 is open at the head sphericalsurface 34 and extends radially inwardly toward the axis A. Each slot 48extends into the convex domed surface 44, but the slots 48 do notintersect or otherwise communicate with one another at the surface 44,leaving a substantial portion of the surface 44 located on and near theaxis A intact for providing adequate surface area for frictionalengagement between the spherical surface 44 and the rod 21 or otherlongitudinal connecting member. With reference to FIGS. 19-21, thedriver 24 is equipped with an inner concave spherical surface 56 andthree outer, evenly spaced prongs 57 sized and shaped for insertion overthe domed surface 44, with the three prongs brining received by thethree radially extending slots 48 of the feature 42. Each prong 57 has asubstantially planar end surface 58 sized and shaped for frictionalengagement with one of the drive slot base surfaces 50, the prongs 57being evenly spaced and illustrated as being fixed to (or may beintegral with) a substantially cylindrical elongate shaft 59. The shaft59 may be part of a larger holding and driving tool system known in theart. The three slots 48 of the drive feature 42 are substantiallyuniform and are sized and spaced such that the slots 48 run centrallythrough every other curvate surface feature 40 with a portion of thesurface feature 40 being cut by the slot 48 remaining on either side ofeach slot 48. Thus the rod 21 or other longitudinal connecting membermay only engage the surface feature 40 on either side of the slot 48 andcannot enter more deeply into a space defined by the drive slot 48 (asshown in FIG. 26, for example). It is foreseen that in otherembodiments, the three-drive slot drive feature 42 on the shank head 8may take other tool-engaging forms and may include, for example, feweror more apertures or slots of various shapes, such as a pair of spacedapart apertures, for example. The illustrated seat or base surface 50 ofeach drive slot 48 of the drive feature 42 is disposed substantiallyperpendicular to the axis A with the drive feature 42 being coaxial withthe axis A. The illustrated drive seats 50 further include beveled orstepped surfaces that may further enhance gripping with the driving tool24 at the prongs 57. As will be described in greater detail below, inoperation, the driving tool prongs 57 are received in the internal driveslots 48, being seated at the base surfaces 50 and engaging the sidewalls 54 for rotating and driving the shank body 6 into the vertebra 17,either before the shank 4 is attached to the receiver 10 or after theshank 4 is attached to the receiver 10, with the shank body 6 beingdriven into the vertebra 17 with the driving tool extending into thereceiver 10 as shown in FIGS. 20 and 21, for example.

The shank 4 shown in the drawings is solid, but in some embodiments maybe cannulated, having a small central bore extending an entire length ofthe shank 4 along the axis A. Such a bore is typically defined by aninner cylindrical wall of the shank 4 having a circular opening at theshank driving tip and an upper opening at the domed top 44. Such a boreis typically coaxial with the threaded body 6 and the upper portion 8.Such a bore provides a passage through the shank 4 interior for a lengthof wire (not shown) inserted into the vertebra 17 prior to the insertionof the shank body 6, the wire providing a guide for insertion of theshank body 6 into the vertebra 17.

To provide a biologically active interface with the bone, the threadedshank body 6 may be coated, perforated, made porous or otherwisetreated. The treatment may include, but is not limited to a plasma spraycoating or other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃(PO₄)₂, tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding.

With particular reference to FIGS. 1 and 5-9, the receiver 10 has agenerally U-shaped appearance with various discontinuous and continuouscurved inner and outer profiles. The receiver 10 has a central axis ofrotation B that is shown in FIG. 1 as being aligned with and the same asthe axis of rotation A of the shank 4, such orientation being desirableduring assembly of the receiver 10, retainer 12 with the shank 4. Afterthe receiver 10 is pivotally attached to the shank 4, the axis B istypically disposed at an angle with respect to the axis A, as shown, forexample, in FIGS. 23-28.

The receiver 10 includes a base or lower body portion 60 that isillustrated as having a cylindrical outer surface, that in someembodiments may include other outer surface geometries, includingcurved, frusto-conical and partially planar. The base 60 defines a boreor inner cavity, generally 61, the base 60 being integral with a pair ofopposed upstanding arms 62 forming a cradle and defining a channel 64between the arms 62 with an upper opening, generally 66. The channel 64is further defined by partially planar interior arm surfaces 67 thattransition to a U-shaped lower saddle or seat 68, the channel 64 havinga width for operably snugly receiving the rod 21 or portion of anotherlongitudinal connector between the arms 62; the channel 64 communicatingwith the base cavity 61.

Each of the arm interior surfaces 67 have formed or machined thereinvarious inner cylindrical profiles, an upper one of which is a partialhelically wound guide and advancement structure 72 located adjacent atop surface or rim 73 of each of the arms 62. In the illustratedembodiment, the guide and advancement structure 72 is a partialhelically wound interlocking flange form configured to mate underrotation with a similar structure on the closure structure 18, asdescribed more fully below. However, it is foreseen that for certainembodiments of the invention, the guide and advancement structure 72could alternatively be a square-shaped thread, a buttress thread, areverse angle thread or other thread-like or non-thread-like helicallywound discontinuous advancement structures, for operably guiding underrotation and advancing the closure structure 18 downward between thearms 62, as well as eventual torquing when the closure structure 18abuts against the rod 21 or other longitudinal connecting member. It isforeseen that the arms could have break-off extensions in someembodiments.

Outer surfaces 74 of each arm 62 are substantially cylindrical andfurther include frusto-conical or curved transition surfaces 75 thatextend radially outwardly to transition to the substantially cylindricalbase 60. A pair of opposed substantially cylindrical through bores 76are located centrally in the arms 72, each bore formed on one of theouter surfaces 74 and extending through the arm inner surface at acylindrical portion 78 thereof located beneath the guide and advancementstructure 72. The opposed bores 76 may be used with tools for holdingthe receiver 10 during assembly with the other components (12 and 4) ofthe bone anchor assembly 1 and during implantation and manipulation ofthe assembly 1 during surgery, for example. It is foreseen that othertool receiving grooves, depressions or apertures may be configured in avariety of shapes and sizes and be disposed at other locations on thereceiver arms 62 and receiver base 60. Below the u-shaped seat 68, thesubstantially cylindrical base 60 eventually tapers inwardly slightlyand then terminates at a substantially planar bottom surface 80 thatpartially defines an opening, generally 81 into the receiver cavity 61.

Returning to the interior surfaces 67 of the receiver arms 62, locatedbelow each guide and advancement structure 72 is a discontinuouscylindrical surface 84 partially defining a run-out feature for theguide and advancement structure 72. The cylindrical surface 84 has adiameter equal to or slightly greater than a greater diameter of theguide and advancement structure 72. Moving downwardly in a directiontoward the base 60, adjacent the cylindrical surface 94 of each arm is arun-out seat or surface 85 that extends inwardly toward the axis B andis substantially perpendicular to the axis B. In other embodiments, thesurface 85 may gently slope downwardly toward the axis B. Adjacent toand located below the surface 85 are planar inner arm surface portionsas well as the centrally located cylindrical surface portion 78 throughwhich the bore 76 extends. Portions of each bore 76 also extend throughthe cylindrical surface 84 and the run-out seat 85. The surface 78terminates at a concave substantially spherical surface 88 that extendsdownwardly along each inner arm 67 and also between and below the curvedsurfaces defining the u-shaped channel seat 68, the surface 88 thusdefining an upper portion of the base cavity 61 where the cavity 61communicates with the u-shaped channel 64. The partially spherical orradiused surface 88 terminates at a largest diameter or hemisphere H2thereof (shown in phantom) with H2 being slightly larger and thusslightly greater in diameter than the diameter D of the shank headsurface 34 having the hemisphere H1. At the hemisphere H2, the surface88 transitions into a cylindrical surface 90. The surface 90 terminatesat an overhang or ceiling surface 92. The surface 92 is annular andperpendicular to the axis B. The surface 92 extends radially outwardlyto a cylindrical surface 94 that terminates at a lower annular seat orledge 96. The surfaces 92, 94 and 96 define an expansion chamber for theretainer 12 as will be described in greater detail below. The surface 92is perpendicular to the cylindrical surface 94. The surface 96 curves orslopes slightly downwardly and inwardly toward and to anothercylindrical surface and 98 that transitions to an annular surface oroperation seat 100 for the retainer 12. The illustrated surfaces 98 and100 are connected by one or more curved or sloping surfaces 99, thesurfaces 98, 99 and 100 operationally capturing and seating the retainer12 against the receiver 10 as will be described in greater detail below;the retainer 12 in turn capturing the shank 8 within the receiver cavity61. The surface 100 terminates at another cylindrical surface 102. Thecylindrical surface 94 has a diameter greater than a diameter of thecylindrical surface 98 that in turn has a diameter greater than adiameter of the cylindrical surface 102. The diameter of the surface 102is substantially the same or slightly greater than the diameter measuredat the hemisphere H2 of the radiused surface 88 that is also thediameter of the cylindrical surface 90. Thus, the surface 102 is sizedto receive the shank head 8 at the greatest diameter D thereof. Thecylindrical surface 102 terminates at an outwardly flaringfrusto-conical surface 104 that terminates at the base surface 80, thesurfaces 102, 104 and 80 forming the lower opening 81 of the receivercavity 61.

With particular reference to FIGS. 1 and 10-12, the rotatable split oropen, ring-like resilient retainer 12 includes the following features: atop discontinuous and substantially planar surface 110; an opposeddiscontinuous substantially planar bottom surface 112 that runs parallelto the top surface 110; a discontinuous outer cylindrical surface 114perpendicular to both the top 110 and bottom 112 surfaces; a curvedconvex transition surface 116 extending between the outer cylindricalsurface 114 and the bottom surface 112; a discontinuous innercylindrical surface 118 spaced from and concentric with the outercylindrical surface 114; an upper inner frusto-conical surface or bevel120 extending from the top surface 110 and running inwardly anddownwardly toward a central axis C of the retainer 12 and terminating atthe inner cylindrical surface 118; and a lower inner frusto-conicalsurface 122 beginning at a termination of the inner cylindrical surface118 and extending downwardly and outwardly away from the axis C andterminating at the bottom surface 112. When assembled with the receiver10, the retainer 12 central axis C is the same as the central axis ofrotation B of the receiver 10. When in a neutral state and in anexpanded state, the retainer 12 top and bottom surfaces aresubstantially uniformly planar and parallel. However, as shown in FIG.13, when the resilient retainer 12 is compressed or contracted duringassembly with the receiver 10, portions of the retainer may overlap aswill be described in greater detail below. This is possible due to theresiliency and small size of the retainer 12 and a small slit or gap,generally 125 located between opposed end surfaces 127 and 128 of theretainer 12. The surfaces 127 and 128 are slightly spaced from oneanother, both the surfaces 127 and 128 being substantially perpendicularto the top surface 110. In other embodiments, the surfaces 127 and 128may not be parallel to one another or both surfaces may be at a similaroblique angle with respect to the top surface 110. It is foreseen thatin some embodiments of the invention, the retainer 12 may have more orfewer planar and cylindrical surfaces. In other embodiments, theretainer 12 may be circular in cross-section, e.g., in the form of asplit ring or wire. In the illustrated embodiment, the retainer 12surface geometry results in the inner upper frusto-conical surface 120,or at least a portion or edge thereof being in operative, fixedfrictional engagement with the spherical surface 34 of the shank head 8when the retainer outer cylindrical surface 114 is pressed against thereceiver cylindrical surface 98 and the retainer outer curved transitionsurface 116 is seated against the receiver transition surface 99 withthe retainer base surface 112 being seated on the receiver annularsurface 100 due to downward pressure of the shank head 8 against theretainer 12 (see, e.g., FIGS. 23-29).

With reference to FIGS. 1 and 22-29, for example, the illustratedelongate rod or longitudinal connecting member 21 (of which only aportion has been shown) can be any of a variety of implants utilized inreconstructive spinal surgery, but is typically a cylindrical, elongatestructure having the outer substantially smooth, cylindrical surface ofuniform diameter. The illustrated rod 21 is sized for use on thecervical spine and thus has a diameter of 3.5 mm and may have a diameteras small as about 3.0 mm and as large as about 4.0 mm. The rod 21 may bemade from a variety of metals, including hard and soft metal alloys andhard and soft or deformable and less compressible plastics, including,but not limited to rods made of elastomeric, polyetheretherketone (PEEK)and other types of materials.

In other embodiments, it is foreseen that longitudinal connectingmembers for use with the assembly 1 may take a variety of shapes,including but not limited to rods or bars of oval, rectangular or othercurved or polygonal cross-section. Some other embodiments may also beused with a tensioned cord. Such a cord may be made from a variety ofmaterials, including polyester or other plastic fibers, strands orthreads, such as polyethylene-terephthalate. Furthermore, thelongitudinal connector may be a component of a longer overall dynamicstabilization connecting member, with cylindrical or bar-shaped portionssized and shaped for being received by the receiver 10. The longitudinalconnecting member may be integral or otherwise fixed to a bendable ordamping component that is sized and shaped to be located betweenadjacent pairs of bone screw assemblies, for example. A dampingcomponent or bumper may be attached to the longitudinal connectingmember at one or both sides of the bone screw assembly. A rod or bar (orrod or bar component) of a longitudinal connecting member may be made ofa variety of materials ranging from soft deformable plastics to hardmetals, depending upon the desired application. Thus, bars and rods maybe made of materials including, but not limited to metal and metalalloys including but not limited to stainless steel, titanium, titaniumalloys and cobalt chrome alloys; or other suitable materials, includingplastic polymers such as polyetheretherketone (PEEK),ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes andcomposites, including composites containing carbon fiber, natural orsynthetic elastomers such as polyisoprene (natural rubber), andsynthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers.

With reference to FIGS. 1 and 22-29, the closure structure or closuretop 18 shown with the assembly 1 is rotatably received between thespaced arms 62 of the receiver 10. It is noted that the closure 18 topcould be a twist-in or slide-in closure structure. The illustratedclosure structure 18 is substantially cylindrical and includes an outerhelically wound guide and advancement structure 142 in the form of aflange that operably joins with the guide and advancement structure 72disposed on the arms 62 of the receiver 10. The flange form utilized inaccordance with embodiments of the present invention may take a varietyof forms, including those described in Applicant's U.S. Pat. No.6,726,689, which is incorporated herein by reference. Although it isforeseen that the closure structure guide and advancement structurecould alternatively be a buttress thread, a square thread, a reverseangle thread or other thread like or non-thread like helically woundadvancement structure, for operably guiding under rotation and advancingthe closure structure 18 downward between the arms 62 and having such anature as to control an amount of splaying of the arms 62 when theclosure structure 18 is advanced into the channel 64, the flange formillustrated herein as described more fully in Applicant's U.S. Pat. No.6,726,689 is preferred as the added strength provided by such flangeform beneficially cooperates with and counters any reduction in strengthcaused by the small size of the cervical screw and longitudinalconnecting member. A single start flange form 142 is illustrated;however, it is foreseen the closure 18 may have two starts withcooperating flange form structure on the receiver arms 62. Theillustrated closure structure 18 also includes a top surface 144 with aninternal drive 146 in the form of an aperture that is illustrated as ahex-shaped internal drive, or may be, for example, a star-shaped or Torxdrive, or other internal drives such as slotted, tri-wing, spanner, twoor more apertures of various shapes, and the like. A driving tool (notshown) sized and shaped for engagement with the internal drive 146 isused for both rotatable engagement and, if needed, disengagement of theclosure 18 from the receiver arms 62. It is also foreseen that in largerembodiments, the closure structure 18 may alternatively include abreak-off head designed to allow such a head to break from a base of theclosure at a preselected torque. Such a closure structure would alsoinclude a base having an internal drive to be used for closure removal.The drive extends all the way through the closure to a bottom surface148 of the closure and may include a rim in some embodiments. The driveprovides a cannulation through bore extending along a central axisthereof and through the top and bottom surfaces thereof. Such a throughbore provides a passage through the closure 18 interior for a length ofwire (not shown) inserted therein to provide a guide for insertion ofthe closure top into the receiver arms 62 in some embodiments anmethods.

The components of the assembly 1, closure top 18 and the rod 21 may bemade from a variety of materials including metals and non-metals,including, but not limited to titanium, titanium alloys, stainlesssteel, cobalt chrome alloys, polymers such as polyetheretherketone(PEEK) and carbon fiber polymers. For example, the assembly may includea retainer 12 preferably made from titanium, a titanium alloy or acobalt chrome alloy and the cooperating receiver and shank may also bemade from any of those materials. A particularly preferred retainer 12is made from a cobalt chrome alloy. However, it is noted when theretainer 12 is made from cobalt chrome, a cooperating receiver 10 andshank 4 should not be made from stainless steel.

With reference to FIGS. 13-18, the receiver 10 and retainer 12 arepreferably assembled at a factory setting that includes tooling forholding and alignment of the component pieces as well as compressing theretainer 12 prior to insertion into the receiver 10. In somecircumstances, the shank 4 is also assembled with the receiver 10 andretainer 12 at the factory. In other instances, it may be more desirablefor the surgical staff to pre-assemble a shank of a desired size and/orvariety (e.g., surface treatment of roughening the upper portion 8and/or hydroxyapatite on the shank 6), with the receiver and retainer.Allowing the surgeon to choose the appropriately sized or treated shank4 advantageously reduces inventory requirements, thus reducing overallcost. Also, it may be desirable in some instances to implant the shank 4into a vertebra first, followed by pressing the retainer (that isalready captured in the receiver) over the shank. In some instances,this may not be desirable due to the small size of the assembly 1 andthe fragile nature of the smaller cervical spine vertebrae for which theassembly 1 is designed.

In addition to being inventory friendly as described above, the assembly1 components may be provided to the end user in a tracking friendly andsterilization friendly manner. The pre-assembled receiver 10/retainer 12combination may be sterilized and individually packaged by the vendor,with each pre-assembly package having a discrete tracking number.Likewise, each shank 4 may be individually sterilized, packaged andgiven a tracking number that may be placed on the package. In otherinstances, an assembly 1 that includes the shank 4, receiver 10 andretainer 12 combination may be provided to the end user in a sterilizedpackage with a tracking number.

Vendor pre-assembly of the receiver 10 with the open ring retainer 12 isshown in FIG. 13. The retainer 12 is bottom loaded into the receiver 10through the receiver opening 81. In order to clear the receiver openingat the cylindrical surface 102, the retainer 12 is compressed with theopposed surfaces 127 and 128 that define the gap or slit 125 initiallypressed toward one another an then maneuvered until a portion of theretainer base surface 112 overlaps onto the retainer top surface 110with one of the end surfaces 127 or 128 located generally above theother end surface as shown in phantom in FIG. 13. Due to the small sizeof the retainer 12, such manipulation of the retainer 12 is possible andthe resulting temporarily overlapping retainer is positioned within thereceiver cavity 61. Once the retainer 12 is moved passed the cylindricalsurface 102, the resilient retainer 12 is released and returns to aneutral or near neutral orientation as shown in solid lines in FIG. 13with the small gap or slit 125 located between the opposed end surfaces127 and 128. In both FIGS. 13 and 14, the now captured retainer 12 isblocked from exiting the bottom opening 81 of the receiver by theannular retainer seating surface 100. Now the retainer 12 is ready to beassembled with the shank 4 at the factory or, alternatively, be shippedto an end user as a sub-assembly (shown in FIG. 13); the end user (e.g.,surgical staff) will thereafter assemble the combination with a desiredshank 4.

With reference to FIGS. 14-18, the shank 4 is shown in various stages ofassembly with the receiver 10 and captured retainer 12. If performed bythe surgical staff, such stages may be performed either before or afterthe shank 4 is implanted into bone. FIGS. 14-18 illustrate a procedurein which the shank 4 is implanted into bone after the shank 4 isconnected to the receiver and retainer sub-assembly. As shown in FIG. 14the shank axis A and the receiver axis B are preferably aligned duringassembly, however, exact axial alignment is not required. It is notedthat although the retainer 12 is now captured within the receiver 10such that very little tilt is allowed and thus most movement of theretainer 12 during assembly is axial or up and down movement along thereceiver axis B, the retainer 12 may also be rotated with respect to thereceiver 10 about the receiver axis B. With further reference to FIG.14, the shank 4 is initially positioned beneath the receiver bottomsurface 80 at the opening 81 and also beneath the retainer bottomsurface 112 with the shank head 8 domed surface 44 initially moved upand through the retainer inner surfaces 122 and 118. With furtherreference to FIG. 15, as the shank head spherical surface 34 abutsagainst the retainer inner frusto-conical surface 122, the shank head 8pushes the retainer 12 top surface 110 into abutment with the receiverceiling surface 92. With reference to FIG. 16, as the shank head 8continues to move upwardly toward the receiver arm u-shaped channel 62,the resilient ring retainer 12 cannot move upwardly and thus expandsoutwardly into the expansion chamber defined by the receiver surfaces92, 94 and 96. Continued upward movement of the shank head surface 34causes the surface 34 to slide first along the frusto-conical surface122 and then the inner cylindrical surface 118 of the retainer 12, thegap 125 widening until the retainer outer cylindrical surface 114 abutsagainst the receive cylindrical surface 94 and the hemisphere H1 movesthrough and past the retainer ring 12. FIG. 16 shows the maximumexpansion of the ring 12 and FIG. 17 shows a resilient return of theretainer 12 to a neutral or near neutral state after the shankhemisphere H1 passes through the retainer 12. FIG. 17 also shows how theretainer ring 12 then drops down to the retainer seat 100. In someembodiments, the shank 4 and the receiver 10 may need to be pulled inopposite directions away from one another to result in a fully seatedretainer ring 12 as shown in FIG. 18. At this time, the shank head 8 iscaptured within the receiver 10, and as is shown in FIG. 18, thespherical surface 34 may be placed into engagement with the retainer 12at the inner surface 120. The spherical surfaces 34 and 44 of the shankare not in engagement with any of the inner surfaces of the receiver 10.Only the retainer ring 12 is engagement with the receiver, but remainsrotatable about the receiver axis B. At this time, the shank 4 is freelypivotable (side to side, forward to back and all pivoting movementstherebetween) and rotatable with respect to the retainer 12 and thusalso with respect to the receiver 10.

With reference to FIGS. 19-21, the fully assembled bone anchor assembly1 made up of the connected shank 4, retainer 12 and receiver 10 areshown with the driver 24 for implanting the bone anchor shank 4 into thevertebra 17. As shown in FIG. 19, the driver 24 is received through thetop opening 66 of the receiver and, as shown in FIGS. 20 and 21 islowered until the three prongs 57 are fully seated in the shankthree-slotted drive 42 with the driver prong base surfaces 58 abuttingagainst the internal drive seating surfaces 50. The driver shaft 59 isthen rotated until the bone screw shank 6 is implanted to a desiredlocation in the vertebra 17. Then the driver 24 is removed out of thetop opening 66 of the receiver 10.

In some procedures, the vertebra 17 may be pre-drilled to minimizestressing the bone and have a guide wire (not shown) inserted therein toprovide a guide for the placement and angle of the shank 4 (inembodiments wherein the shank is cannulated) with respect to thevertebra. A further tap hole may be made using a tap with the guide wireas a guide. Then, the assembly 1 may be threaded onto the guide wireutilizing the cannulation bore. The shank 4 is then driven into thevertebra using the wire as a placement guide. It is foreseen that theshank and other bone screw assembly parts, the rod 21 (also having acentral lumen in some embodiments) and the closure top 18 (also with acentral bore) can be inserted in a percutaneous or minimally invasivesurgical manner, utilizing guide wires. As indicated earlier, ifdesired, the shank 4 alone may be driven into the vertebra 17 utilizingthe pronged driver 24 without the remainder of the assembly 1, followedby pressing the receiver 10 and captured open retainer 12 onto the shankhead 8. In such embodiments, the shank 4 may either be driven to adesired final location or may be driven to a location slightly above orproud to provide for ease in assembly with the pre-assembled receiver 10and retainer 12. Thereafter, the shank 4 may be driven deeper into thevertebra 17 as illustrated in FIGS. 19-21 and previously describedherein.

At this time and with reference to FIGS. 23-29, the receiver 10 may bearticulated to a variety of angular positions with respect to the shank4 prior to insertion of the rod 21 or closure top 18. Also withreference to FIGS. 22-29, the rod 21 is eventually positioned in an openor percutaneous manner in cooperation with the at least two bone screwassemblies 1. The closure structure 18 is then inserted into andadvanced between the arms 62 of each of the receivers 10. The closurestructure 18 is rotated, using a tool engaged with the inner drive 146until a selected pressure is reached (typically about 40-50 inch poundsof torque) at which point the rod 21 frictionally engages and fixesagainst the domed surface 44 of shank head 8. The rod 21 pressing downon the surface 44 also urges the shank upper portion 8 spherical surface34 toward the retainer inner surface 120 or outer edge thereof and intolocking engagement therewith, the retainer 12 frictionally abutting andexpanding outwardly against the receiver 10 at one or more of thesurfaces 98, 99 and 100.

FIG. 22 shows the assembly 1 in a locked position with the rod 21 andclosure top 18 wherein the shank 4 axis A is substantially aligned withreceiver axis B. FIGS. 23 and 24 show the assembly 1 in an alternativelocked position with the rod 21 and the closure top 18 wherein thereceiver 10 had been previously pivoted with respect to the shank 4 to aforty-four degree angle with the rod 21 being substantially received inone of the concave surface cut-outs 40 formed in the spherical surface34 to allow for such extended pivot of the shank with respect to thereceiver (shown in the sagittal plane and with the shank directedcaudally). FIGS. 25 and 26 illustrate the same assembly in an oppositeforty-four degree angulation of the receiver with respect to the shankin a sagittal plane/cephalic direction. In such angulation, the rod 21is also substantially received on one of the concave surface features 40that includes a drive slot 48. However, as shown in FIG. 26, the rod 21is adequately supported by remaining portions of the feature 40 and doesnot extend into the drive slot 48. Furthermore in both the cephalic andcaudally directed extended angles, the spherical surface portions 34located between the carved out features 40 are adequate to securely holdthe shank head 8 in a fixed position against the retainer 12. Withreference to FIG. 27, the receiver 10 has been pivoted with respect tothe shank 4 (prior to locking of the closure 18 onto the rod 21) to aforty-four degree angle in the transverse plane. Finally, with referenceto FIGS. 28 and 29, a twenty-four degree angulation between the shank 4and the receiver 10 is shown along with rotation of the shank, showinghow the rod may in some instances be fixed in position against the dome44 and the edge 36 of the spherical surface 34.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A polyaxial bone screw assembly for surgical implantation,the assembly comprising: a receiver having a base and opposed arms, thebase having an inner cavity and the arms forming a longitudinalconnecting member receiving channel, the channel communicating with theinner cavity; a shank having a threaded body and a head, the threadedbody for implantation into bone and the head being captured within theinner cavity, the shank being pivotable with respect to the receiver;and a separate retaining structure located within the inner cavity thatretains the shank head within the receiver, wherein: a) the inner cavityis partially defined by a lower seat and partially defined by aretaining structure expansion chamber located above the lower seat, thelower seat sized and shaped for operatively frictionally holding theretaining structure; b) the retaining structure being open andresilient, the shank head being bottom-loadable into the receiver, theretaining structure expandable about the head in the expansion chamberduring loading of the head into the receiver; and c) the shank headhaving a first convex surface with a first radius that is sized andshaped for direct contact with a longitudinal connecting member toreceive direct downward force from direct engagement with thelongitudinal connecting member, the shank having a second lower convexsurface having a second radius that is larger than the first radius, thesecond lower convex surface being operationally spaced from the receiverand in direct engagement with the retaining structure and fixed theretowhen the longitudinal connecting member places direct downward force onthe first convex surface, the second lower convex surface terminating atan upper perimetric edge and wherein one and up to a plurality ofconcave surface features are formed into the second lower convex surfaceat and near the upper perimetric edge, each concave surface featuresized and shaped for receiving a portion of the longitudinal connectingmember to allow for an increased angle of pivot between the shank andthe receiver, the upper perimetric edge being made discontinuous by theone and up to plurality of concave surface features.
 2. The polyaxialbone screw assembly of claim 1 wherein the second lower convex surfaceis substantially spherical and has a hemisphere, the upper perimetricedge located above the hemisphere.
 3. The polyaxial bone screw assemblyof claim 1 wherein the upper perimetric edge forms a discontinuouscircle.
 4. The polyaxial bone screw assembly of claim 1 wherein both thefirst convex surface and the second lower convex surface aresubstantially spherical.
 5. The polyaxial bone screw assembly of claim 1wherein the first convex surface has an internal drive formed thereon.6. The polyaxial bone screw assembly of claim 1 wherein an internaldrive slot is formed in the one and up to a plurality of concave surfacefeatures.
 7. The polyaxial bone screw assembly of claim 1 wherein theopen retaining structure is up-loadable into the inner cavity.
 8. Thepolyaxial bone screw assembly of claim 7 wherein the retaining structureincludes surfaces that overlap during uploading into the inner cavity.9. A polyaxial spinal bone screw assembly for receiving and fixingplacement of a longitudinal connecting member, the assembly comprising:a) a bone screw shank having a body integral with a shank upperstructure, the shank upper structure having a top first surface that isconvex spherically shaped and having a first radius, a lower secondsurface that is convex partially spherically shaped and having a secondradius, a third annular surface extending outwardly from the top firstsurface and terminating at the lower second surface and one and up to aplurality of concave surface features formed in the lower second and theannular third surfaces; b) a receiver having a pair of arms forming achannel, the receiver also having a cavity with a concave partiallyspherically shaped surface adapted to allow pivotal movement of the topfirst and the lower second surfaces of the shank during positioning anda lower opening to an exterior of the receiver opposite the pair ofarms, the cavity communicating with the channel, the cavity furtherdefined by a lower seat and an expansion area located above the lowerseat, the shank upper structure being uploaded and received in thecavity through the lower opening; c) an open and resilient ring-likeretainer receivable in the cavity and outwardly biased against thereceiver in fixed relation thereto at the lower seat of the receiverwhen the shank upper structure is in the receiver, the retainerexpanding about the shank upper structure when the shank upper structureis loaded into the receiver through the lower opening and having aretainer surface sized and shaped to operationally frictionally engagethe lower second surface of the shank and retain the shank upperstructure within the cavity, the shank upper structure sized and shapedto extend above the retainer with the top first surface of the shankreceiving direct downward force from contact with the longitudinalconnecting member so as to lock an angular position of the receiverrelative to the shank, the assembly having an unlocked position whereinthe shank upper structure is in sliding, pivotable relation with theretainer and a locked position wherein the lower second surface is infixed frictional engagement with the retainer surface; and wherein d)when in an unlocked position a portion of the rod may be received in anarea defined by one of the one and up to a plurality of concave surfacefeatures to provide an increased angle of articulation between the shankand the receiver and another portion of the rod may then be fixed intolocking engagement with the top first convex surface of the shank. 10.The polyaxial spinal bone screw assembly of claim 9 wherein the topfirst convex surface has an internal drive formed thereon.
 11. Thepolyaxial spinal bone screw assembly of claim 9 wherein an internaldrive slot is formed in one and up to a plurality of the concave surfacefeatures.
 12. The polyaxial spinal bone screw assembly of claim 9wherein the retainer is up-loadable into the cavity.
 13. A polyaxialbone anchor, the improvement comprising a) a receiver defining a chambercommunicating with a channel, the channel sized and shaped for receivinga portion of a longitudinal connecting member, the chamber defined inpart by a lower seat and in part by an expansion area located betweenthe lower seat and the channel; b) a shank having a shank upper portionwith a first surface and a second surface, the first and second surfacesbeing convex partially spherical shaped, and a plurality of spacedconcave surface features formed in the second surface, each concavesurface feature defining an area for receiving a portion of thelongitudinal connecting member, the second surface being larger than thefirst surface, the first surface configured for direct frictionalengagement with the longitudinal connecting member, the second surfacehaving a hemisphere and terminating at a spheric edge located above thehemisphere, the spheric edge being located below the first surface, thespaced concave surface features located about and running through thespheric edge; and c) an open retainer located in the chamber, theretainer expandable in the chamber about the shank upper portion at theexpansion area and receiving the upper portion therethrough to capturethe upper portion in the chamber, the retainer being in an expandedstate and fixed between the second surface of the shank upper portionand the lower seat of the receiver when the shank is in a frictionallyfixed orientation with respect to the receiver.